Open Data supplied by Natural Environment Research Council (NERC)

Instrument Description ISSS-08

CTD Unit and Auxiliary Sensors

The CTD was a standard SeaBird 9/11 plus , mounted on a rosette with 12 Niskin bottles each with a volume of 6.7 litres. At some selected stations additional 20 litre GoFlo bottle were mounted on the rosette providing extra larger volume sampling.

The table below lists detailed information about the various sensors.

Sensor

Model

Serial number

Pressure transducer

SBE-911 plus Digiquartz pressure sensor

0613

Conductivity sensor

SBE 4C

2456

Temperature sensor

SBE 3

4098

Turbidity sensor

Wetlabs turbidity sensor ECO NTU

NTURTD-126

Sea-Bird Electronics SBE 911 and SBE 917 series CTD profilers

The SBE 911 and SBE 917 series of conductivity-temperature-depth (CTD) units are used to collect hydrographic profiles, including temperature, conductivity and pressure as standard. Each profiler consists of an underwater unit and deck unit or SEARAM. Auxiliary sensors, such as fluorometers, dissolved oxygen sensors and transmissometers, and carousel water samplers are commonly added to the underwater unit.

Underwater unit

The CTD underwater unit (SBE 9 or SBE 9 plus ) comprises a protective cage (usually with a carousel water sampler), including a main pressure housing containing power supplies, acquisition electronics, telemetry circuitry, and a suite of modular sensors. The original SBE 9 incorporated Sea-Bird's standard modular SBE 3 temperature sensor and SBE 4 conductivity sensor, and a Paroscientific Digiquartz pressure sensor. The conductivity cell was connected to a pump-fed plastic tubing circuit that could include auxiliary sensors. Each SBE 9 unit was custom built to individual specification. The SBE 9 was replaced in 1997 by an off-the-shelf version, termed the SBE 9 plus , that incorporated the SBE 3 plus (or SBE 3P) temperature sensor, SBE 4C conductivity sensor and a Paroscientific Digiquartz pressure sensor. Sensors could be connected to a pump-fed plastic tubing circuit or stand-alone.

Temperature, conductivity and pressure sensors

The conductivity, temperature, and pressure sensors supplied with Sea-Bird CTD systems have outputs in the form of variable frequencies, which are measured using high-speed parallel counters. The resulting count totals are converted to numeric representations of the original frequencies, which bear a direct relationship to temperature, conductivity or pressure. Sampling frequencies for these sensors are typically set at 24 Hz.

The temperature sensing element is a glass-coated thermistor bead, pressure-protected inside a stainless steel tube, while the conductivity sensing element is a cylindrical, flow-through, borosilicate glass cell with three internal platinum electrodes. Thermistor resistance or conductivity cell resistance, respectively, is the controlling element in an optimized Wien Bridge oscillator circuit, which produces a frequency output that can be converted to a temperature or conductivity reading. These sensors are available with depth ratings of 6800 m (aluminium housing) or 10500 m (titanium housing). The Paroscientific Digiquartz pressure sensor comprises a quartz crystal resonator that responds to pressure-induced stress, and temperature is measured for thermal compensation of the calculated pressure.

Additional sensors

Optional sensors for dissolved oxygen, pH, light transmission, fluorescence and others do not require the very high levels of resolution needed in the primary CTD channels, nor do these sensors generally offer variable frequency outputs. Accordingly, signals from the auxiliary sensors are acquired using a conventional voltage-input multiplexed A/D converter (optional). Some Sea-Bird CTDs use a strain gauge pressure sensor (Senso-Metrics) in which case their pressure output data is in the same form as that from the auxiliary sensors as described above.

Deck unit or SEARAM

Each underwater unit is connected to a power supply and data logging system: the SBE 11 (or SBE 11 plus ) deck unit allows real-time interfacing between the deck and the underwater unit via a conductive wire, while the submersible SBE 17 (or SBE 17 plus ) SEARAM plugs directly into the underwater unit and data are downloaded on recovery of the CTD. The combination of SBE 9 and SBE 17 or SBE 11 are termed SBE 917 or SBE 911, respectively, while the combinations of SBE 9 plus and SBE 17 plus or SBE 11 plus are termed SBE 917 plus or SBE 911 plus .

WETLabs ECO NTU turbidity sensor

WET Labs offers the Environmental Characterization Optics (ECO) series of meters that incorporate a common set of options with a single basic design to make them ideal for a wide variety of deployments. The NTU provides:

Unparalleled sensitivity in an optical scattering measurement at 700 nm for determining turbidity. An instrument that is easily integrated into CTD packages and provides a reliable turbidity measurement that is not affected by Colored Dissolved Organic Matter (CDOM) concentration.

The ECO-NTU range consists of five models that all operate at 700 nm but have slight differences, as listed below:

BODC Processing ISSS-08

Reformatting

The data arrived at BODC as 134 ASCII files, representing all of the CTD casts taken during the cruise. Data was reformatted to BODC internal QXF format (subset of NETcdf). The following table shows how the variables within the ASCII files were mapped to the appropriate BODC parameter codes.

Originator's Parameter Name

Units

Description

BODC Parameter Code

Units

Comments

Pressure

dbar

Pressure of water body on profiling pressure sensor

PRESPR01

dbar

-

Temperature [ITS-90]

°C

Temperature of water column by CTD

TEMPCU01

°C

-

Salinity, Practical

-

Practical salinity of the water body by CTD

PSALCC01

-

Generated by Sea-Bird software from CTD temperature and conductivity data

Turbidity sensor

Volts

Instrument output by WET Labs optical backscatter meter

NVLTWL01

Volts

-

Screening

Reformatted CTD data were visualised using the in-house graphical editor EDSERPLO. No data values were edited or deleted. Quality control flags were applied to data as necessary.

References

UNESCO, 1981. Background papers and supporting data on the International Equation of State of Seawater 1980. UNESCO Technical Papers in Marine Science No. 38, 192pp

Originator's Data Processing ISSS-08

Sampling Strategy

The motivation for ISSS-08 was to alleviate the scarcity of observational data on transport and processing of water, sediment and carbon on the East Siberian Arctic Shelves (ESAS). The ESAS, composed of Laptev, East Siberian and Russian part of Chukchi Sea, is the worlds largest continental shelf and at the same time the most understudied part of the Arctic Ocean. A complex sampling program was accomplished during the 50-days ISSS-08 cruise, including studying the Pacific inflow through the Herald Canyon and remnants of salty and cold bottom waters on the shelf break.

Data Processing

The data has been processed using the Seabird standard software package through the following routines:

Field Calibrations

GEOTRACES

Introduction

GEOTRACES is an international programme sponsored by SCOR which aims to improve our understanding of biogeochemical cycles and large-scale distribution of trace elements and their isotopes (TEIs) in the marine environment. The global field programme started in 2009 and will run for at least a decade. Before the official launch of GEOTRACES, fieldwork was carried out as part of the International Polar Year (IPY)(2007-2009) where 14 cruises were connected to GEOTRACES.

GEOTRACES is expected to become the largest programme to focus on the chemistry of the oceans and will improve our understanding of past, present and future distributions of TEIs and their relationships to important global processes.

This initiative was prompted by the increasing recognition that TEIs are playing a crucial role as regulators and recorders of important biogeochemical and physical processes that control the structure and productivity of marine ecosystems, the dispersion of contaminants in the marine environment, the level of greenhouse gases in the atmosphere, and global climate.

Scientific Objectives

GEOTRACES mission is: To identify processes and quantify fluxes that control the distribution of key trace elements and isotopes in the ocean, and to establish the sensitivity of these distributions to changing environmental conditions.

Three overriding goals support the GEOTRACES mission

Determine ocean distributions of selected TEIs at all major ocean basins

Evaluate the sources, sinks, and internal cycling of these TEIs and thereby characterize more completely their global biogeochemical cycles

Provide a baseline distribution in the Polar Regions as reference for assessing past and future changes.

These goals will be pursued through complementary research strategies, including observations, experiments and modelling.

Fieldwork

The central component of GEOTRACES fieldwork will be a series of cruises spanning all Ocean basins see map below.

Three types of cruise are required to meet the goals set out by GEOTRACES. These are

Section cruises - These will measure all the key parameters (see below) over the full depth of the water column. The sections were discussed and approved by the International GEOTRACES Scientific Steering Committee at the basin workshops.

Process Studies - These will investigate a particular process relevant to the cycling of trace metal and isotopes. They must follow the "Criteria for Establishing GEOTRACES Process Studies" and be approved by the International GEOTRACES Scientific Steering Committee.

Cruises collecting GEOTRACES compliant data - These will collect some trace element or isotope data. They must follow the GEOTRACES Intercalibration and Data Management protocols

IPY-GEOTRACES

The IPY-GEOTRACES programme comprised of 14 research cruises on ships from 7 nations; Australia, Canada, France, Germany, New Zealand, Japan and Russia. The cruises will not be classified in the same way as the full GEOTRACES programme since the intercalibration protocols and data management protocols had not been established before the start of the IPY. But IPY-GEOTRACES data will still be quality controlled by GDAC and in the majority of cases verified versus Intercalibration standards or protocols.